Safety vent structure for extracorporeal circuit

ABSTRACT

In general, this disclosure relates to extracorporeal fluid circuits. In some aspects, an air-release device for allowing air to be released from a liquid in extracorporeal circuitry includes an elongate chamber having a bottom region and a top region and a fluid entry port and fluid exit port at or near the bottom region. The air release device also includes a vent structure at or near the top region of the elongate chamber that includes a porous material capable of swelling when moistened such that the vent structure can inhibit liquid from escaping the air-release device during use.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application and claims priority toU.S. application Ser. No. 12/233,111, filed Sep. 18, 2008, which claimsthe benefit of the filing date of U.S. Provisional Application No.60/973,730, filed Sep. 19, 2007. The contents of U.S. application Ser.Nos. 12/233,111 and 60/973,730 are incorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to extracorporeal fluid circuits.

BACKGROUND

Hemodialysis removes toxic substances and metabolic waste from thebloodstream using an extracorporeal circuit with components designed toperform ultrafiltration and diffusion on the blood. Before the blood isreturned to the body, air bubbles are removed from the blood to inhibitembolisms.

SUMMARY

In one aspect, an extracorporeal medical fluid circuit component isdescribed. The component includes a vent assembly. A vent structureadjacent to a micro-porous membrane forms the assembly. The ventstructure is porous, but expands when the vent structure becomes wet,thereby closing off the pores and inhibiting (e.g., preventing) fluidfrom flowing through the vent structure. The vent structure alsoprotects the membrane from becoming wet, such as from condensation. Thecomponent is capable of being used in an extracorporeal medical fluidcircuit.

In another aspect, a transducer protector includes a body that defines afluid pathway. A vent assembly is disposed in the fluid pathway. Thevent assembly includes a vent structure and a micro-porous membrane. Thevent structure is porous, but expands when the vent structure becomeswet, thereby closing off the pores and inhibiting (e.g., preventing)fluid from flowing through the vent structure. The vent structure alsoprotects the membrane from becoming wet, such as from condensation. Thetransducer protector is capable of being connected in fluidcommunication with a fluid circuit and a pressure transducer such thatthe vent assembly inhibits liquid flowing in the fluid circuit fromcontacting the pressure transducer.

In a further aspect, an extracorporeal medical fluid circuit apparatus,e.g., for removing air from a bodily liquid in extracorporeal circuitryused in a hemodialysis machine, is described. The apparatus includes achamber having a fluid entry port, a fluid exit port, and a ventassembly. The vent assembly includes a micro-porous membrane and a ventstructure adjacent to the micro-porous membrane. The vent structureincludes a porous material that is capable of swelling when moistened.The fluid entry port and the fluid exit port are arranged to allowliquid to pass through the chamber from the entry port to the exit portso as to fill the chamber with the liquid when back pressure is applied,and the vent assembly is arranged to allow gas to exit the chamber asthe liquid passes through the chamber.

In yet another aspect, an integrated fluid circuit component adapted toremovably seat in a dialysis machine is described. The componentincludes a rigid body having a substantially flat main portion and aplurality of recessed portions extending from the flat main portion anda flexible backing covering at least one of the of recessed portions. Afirst recessed portion of the plurality of recessed portions forms achamber. A second recessed portion of the plurality of recessed portionsforms a first channel that is in fluid communication with the chamber,and a third recessed portion of the plurality of recessed portions formsa second channel in fluid communication with the chamber. The componentalso includes a vent assembly that is in fluid communication with thechamber. The vent assembly includes a micro-porous membrane and a ventstructure.

In yet another aspect, a dialysis system is described. The systemincludes a machine body, a pump on the machine body, and fluid circuitry(e.g., tubes) in fluid communication with the pump. The pump isconfigured to push fluid through the circuitry. The system also includesa vent assembly in fluid communication with the fluid circuitry. Thevent assembly includes a micro-porous membrane and a vent structureadjacent to the micro-porous membrane. The vent structure includes aporous material that is capable of swelling when moistened.

In another aspect, a method of removing air from a bodily liquid indialysis circuitry is described. A chamber with an entry port, an exitport, a micro-porous membrane and a vent structure is provided. A firstliquid is passed through the entry port, filling the chamber so thatsubstantially no air remains in the chamber. A second liquid is passedthrough the entry port, forcing a portion of the first liquid out of anexit port of the chamber and forming a liquid-liquid interface betweenthe first and second liquids. Any gas bubbles contained in the secondliquid can be forced out of the chamber through the micro-porousmembrane and the vent structure.

Embodiments of the disclosed methods, systems and devices may includeone or more of the following features.

The vent structure can have an average pore size of about 15 microns toabout 45 microns.

The vent structure can include a polymer such as polyethylene (e.g.,high density polyethylene (HDPE)), polypropylene, or polystyrene.

The vent structure can include a swelling agent such ascarboxymethylcellulose (CMC), methyl-ethyl-cellulose or other similarswelling agents.

The vent structure can include a blend of a polymer and a swellingagent.

The vent structure can have a thickness greater than a thickness of themicro-porous membrane.

The micro-porous membrane can have an average pore size of about 0.05microns to about 0.45 microns (e.g., about 0.22 microns or about 0.2microns).

The micro-porous membrane can be held by a plastic ring (e.g., by insertmolding, heat welding, ultrasonic welding, adhesive, clamping, etc.) andthe assembly can also include an insert for holding the micro-porousmembrane adjacent to the vent structure.

In some embodiments, a structure or assembly can include a plastic ringinto which the micro-porous membrane is press-fit, wherein the ringsurrounds the vent structure and retains the vent structure adjacent tothe micro-porous membrane.

The vent structure can include a first porous layer adjacent to themicro-porous membrane, and a second porous layer adjacent to the firstporous layer.

The second porous layer can include a porous material that is capable ofswelling when moistened.

The first porous layer can also include a porous material that iscapable of swelling when moistened.

The second porous layer can have a greater propensity to swell in thepresence of moisture than the first porous layer.

The second porous layer can have an average pore size that is greaterthan an average pore size of the first porous layer. For example, thefirst porous layer can have an average pore size of about 10 microns,and the second porous layer can have an average pore size of about 30microns.

The second porous layer can include about 5% to about 50% by weightcarboxymethylcellulose (e.g., about 10% by weightcarboxymethylcellulose).

The first porous layer can include 0% to about 10% by weightcarboxymethylcellulose (e.g., less than 5% by weightcarboxymethylcellulose).

The extracorporeal medical fluid circuit component can be configured foruse in an air release chamber.

The extracorporeal medical fluid circuit component can be configured foruse in a transducer protector.

The extracorporeal medical fluid circuit component can be configured foruse in a blood circuit. The blood circuit can be capable of being usedwith a dialysis machine.

The micro-porous membrane can be between the vent structure and thechamber.

The vent structure can include porous material that is capable ofswelling when moistened.

The dialysis system can include a pressure transducer and a transducerprotector that includes the vent assembly.

The transducer protector can be disposed between, and in fluidcommunication with, the circuitry and the pressure transducer.

Passing the second liquid through the entry port can include passingmoisture from the second liquid through the micro-porous membrane andallowing the moisture to pass through the vent structure, causing thevent structure to swell.

Other aspects, features, and advantages are in the description,drawings, and claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an extracorporeal fluid circuit forhemodialysis system.

FIG. 2 is schematic view of a pressure sensor assembly.

FIG. 3A is side view of a transducer protector.

FIG. 3B is a cross-sectional side view of the transducer protector ofFIG. 3A.

FIG. 4A is a cross-sectional side view of a first part of the transducerprotector of FIG. 3A.

FIG. 4B is a cross-sectional side view of a second part of thetransducer protector of FIG. 3A.

FIGS. 5A-5C are cross-sectional views illustrating the assembly of thetransducer protector of FIG. 3A.

FIGS. 6A and 6B illustrate a dialysis machine measuring pressurepatterns of an extracorporeal blood circuit.

FIG. 7 is a schematic cross-sectional view of an air release chamberwith a vent assembly.

FIG. 7A is a schematic top view of the air release chamber of FIG. 7.

FIG. 7B is a schematic bottom view of the air release chamber of FIG. 7.

FIG. 7C is a schematic perspective view of the air release chamber ofFIG. 7.

FIGS. 7D, 7E, and 7F are each schematic cross-sectional views of airrelease chambers.

FIG. 8 is a schematic top view of a hydrophobic filter assembly.

FIG. 8A is a schematic cross-sectional view of the hydrophobic filterassembly of FIG. 8, taken along line 8A-8A.

FIG. 9 is a schematic top view of a vent structure.

FIG. 9A is a cross-sectional view of the vent structure of FIG. 9, takenalong line 9A.

FIG. 10 is a schematic top view of an insert.

FIG. 10A is a cross-sectional view of the insert of FIG. 10, taken alongline 10A-10A.

FIG. 10B is a side view of the insert of FIG. 10.

FIG. 11 is a schematic top view of a retainer.

FIG. 11A is a cross-sectional view of the retainer of FIG. 11, takenalong line 11A-11A.

FIG. 12 is a schematic cross-sectional view of a vent assembly.

FIG. 13 is a schematic side view of a chamber and port cap than can beassembled to form a bottom entry/bottom exit chamber.

FIG. 14 is a schematic side view of a bottom entry/bottom exit chamber.

FIG. 15 is a schematic cross-sectional view of a bottom entry/bottomexit chamber and a vent assembly.

FIG. 16 is a schematic side view of a bottom entry/bottom exit chamberwith a vent assembly.

FIG. 17 is a schematic top view of a filter assembly.

FIG. 17A is a cross-sectional view of the filter assembly of FIG. 17,taken along line 17A-17A.

FIG. 17B is a side view of the filter assembly of FIG. 17.

FIG. 18 is a schematic cross-sectional view of a vent assembly.

FIG. 19 is a schematic side view of a bottom entry/bottom exit chamberand a vent assembly.

FIG. 20 is a schematic cross-sectional view of a bottom entry/bottomexit chamber and a vent assembly.

FIG. 21 is a schematic side view of a bottom entry/bottom exit chamberand a vent assembly.

FIG. 22 is a flow diagram for using an air release chamber in anextracorporeal circuit.

FIG. 23 is a schematic diagram of the blood flow path through an airrelease chamber.

FIG. 24 is a schematic diagram of an extracorporeal circuit for ahemodialysis system including pre-pump and post-pump arterial pressuresensor assemblies and a venous pressure sensor assembly.

FIG. 25 is a schematic cross-sectional view of an air release chamberwith a vent assembly having a multilayer vent structure.

FIG. 26 is a plan view of an integrated extracorporeal circuit.

FIG. 26A is a cross sectional view of the integrated extracorporealcircuit of FIG. 26, take along line 26A-26A.

FIG. 27 is a perspective view of the integrated extracorporeal circuitof FIG. 26.

DETAILED DESCRIPTION

A fluid circuit, such as an extracorporeal fluid circuit used infiltering blood from a patient during hemodialysis, can be provided withone or more self-sealing vent assemblies to inhibit (e.g., prevent)fluids flowing within the circuit from coming into contact with thesurrounding, external atmosphere and/or coming into contact with, andpossibly contaminating, neighboring devices. The self-sealing ventassemblies can also inhibit (e.g., prevent) foreign particles andorganisms from the external atmosphere from coming into contact withliquid flowing within the fluid circuit.

System Overview

Referring to FIG. 1, an extracorporeal circuit 100 includes tubingthrough which the blood flows and components for filtering andperforming dialysis on the blood. Blood flows from a patient 105 througharterial tubing 110. Blood drips into a drip chamber 115 where aconnecting tube 116 from the drip chamber 115 attaches to an arterialpressure sensor assembly 120 on a hemodialysis machine 50 thatdetermines the pressure of the blood on the arterial side of the circuit100. The arterial pressure sensor assembly 120 includes a pressuretransducer 130, which can be mounted within a dialysis machine 50, sothat the pressure of blood flowing through the circuit 100 on thearterial side can be monitored. The arterial pressure sensor assembly120 also includes a transducer protector 140, which carries aself-sealing vent assembly 141 (FIG. 3B) that includes a micro-porousmembrane 144 (FIG. 3B) and a liquid activated self-sealing ventstructure 146 (FIG. 3B). The vent assembly 141 helps to protect thepressure transducer 130, and the dialysis machine 50 in which it ismounted, from direct contact with blood flowing within theextracorporeal circuit 100. In the event that the micro-porous membrane144 ruptures, blood will come into contact with the liquid activatedself-sealing vent structure 146. The vent structure 146 will seal, and,by sealing, will inhibit (e.g., prevent) the dialysis machine 50 frombecoming contaminated, and will allow the machine 50 to detect a failurevia analysis of pressure patterns.

A pump 160, such as a peristaltic pump, forces the blood to continuealong the path through the circuit 100. The blood then flows to adialyzer 170, which separates waste products from the blood.

After passing through the dialyzer 170, the blood flows through venoustubing 180 towards an air release chamber 230 in which gas (e.g., air)in the blood can escape before the blood continues to the patient 105.During treatment, should air be present in the blood, the blood with airbubbles flows in through the bottom of the air release chamber 230. Theupper motion of the blood is impeded by gravity and becomes stagnant,while the air continues to the top of the chamber 230 where it is ventedout to the atmosphere through another self-sealing vent assembly 270.The vent assembly 270 of the chamber 230 includes a micro-porousmembrane and a self-sealing vent. The micro-porous membrane normallyoperates to inhibit liquids within the chamber from coming into contactwith the atmosphere. However, in the event that the micro-porousmembrane ruptures, liquid will come into contact with the self-sealingvent, which will self seal and inhibit (e.g., prevent) the blood fromcoming into contact with the atmosphere.

After leaving the chamber 230, the blood travels through a venous line190 and back to the patient 105.

Pressure Transducer Assembly

As shown in FIG. 2, the pressure transducer assembly 120 includes thepressure transducer 130 and the transducer protector 140. Referring toFIGS. 3A and 3B, the transducer protector 140 includes a body 143 thatdefines a fluid pathway. The body 143 includes a vent assemblycompartment 142 in which the micro-porous membrane 144 and theself-sealing vent structure 146 are disposed. A first open end 148 canbe connected to the dialysis machine 50, e.g., via a machine fitment 52(FIG. 2) and tubing 117, and provides for fluid communication betweenthe pressure transducer 130 and the vent assembly compartment 142. Asecond open end 149 can be connected to the tubing (e.g., connectingtube 116) of the extracorporeal circuit 100 (FIG. 1) to provide forcommunication between the vent assembly compartment 142 and bloodflowing within the circuit 100. This arrangement allows gas (e.g., air)to pass through the vent assembly 141 from the second open end 149toward the first open end 148, while inhibiting the passage of blood,and thereby allows the pressure transducer 130 to measure changes in airpressure.

The micro-porous membrane 144 allows gas (e.g., air) to pass through thevent assembly compartment 142, but impedes the flow of liquid, therebyinhibiting or preventing the blood from directly contacting, andpossible contaminating, the pressure transducer 130 on the opposite sideof the vent assembly compartment 142. The micro-porous membrane 144 canalso help to inhibit (e.g., prevent) foreign particles and organismsfrom entering the extracorporeal circuit 100 from the transducer side ofthe vent assembly compartment 142.

The micro-porous membrane 144 includes a hydrophobic material, such aspolytetrafluoroethylene (PTFE) (e.g., expanded polytetraflouroethylene(ePTFE)) backed by a mesh material. In some embodiments, the membrane144 is a fibrous carrier with a matted and woven layer on top of whichePTFE or other micro-porous material is applied. A suitable membrane hasan average pore size of about 0.05 to about 0.45 microns (e.g., about0.22 microns or about 0.2 microns). Suitable membranes are availablefrom Pall Corporation, East Hills, N.Y., under the Versapor® mark andfrom W. L. Gore & Associates, Inc., Newark, Del.

The self-sealing vent structure 146 is a solid porous block, having anaverage pore size of about 15 to about 45 microns, that allows air topass through the vent assembly compartment 142. In some embodiments, theself-sealing vent structure 146 is formed of a blend of polyethylene(e.g., high density polyethylene (HDPE)) and carboxymethylcellulose(CMC), a blend of polystyrene and methyl-ethyl-cellulose or ofpolypropylene- or polyethylene-based porous material. Such materials areavailable from Porex Corporation, Fairburn, Ga., such as EXP-816, whichis a product containing 90% by weight polyethylene and 10% by weightcarboxymethylcellulose with an average pore size of about 30 microns toabout 40 microns. However, other percentages of the materials can beused, as well as other materials and other pore sizes. For example, thevent structure 146 can include about 80% to about 95% by weight highdensity polyethylene and about 5% to about 20% by weightcarboxymethylcellulose.

Referring to FIGS. 4A and 4B the body 143 of the transducer protector140 can be formed from two parts. As shown in FIG. 4A, a first part 150defines the first open end 148 and a first portion 151 of the ventassembly compartment 142. As shown in FIG. 4B, a second part 152 definesthe second open end 149 and a second portion 153 of the vent assemblycompartment 142. The first and second parts 150, 152 of the transducerprotector 140 can be formed of one or more medical grade materials.Plastics, such as polyvinylchloride, polycarbonate, polyolefins,polypropylene, polyethylene or other suitable medical grade plastic canbe used because of their ease of manufacturing, ready availability anddisposable nature. The first and second parts 150, 152 of the transducerprotector can be separately formed, such as by molding (e.g., extruding,blow molding or injection molding).

The first and second parts 150, 152 of the transducer protector 140 eachinclude an associated sidewall 154, 155. The sidewalls 154, 155 of therespective first and second parts 150, 152 help to retain themicro-porous membrane 144 and the self-sealing vent structure 146 withinthe vent assembly compartment 142 following assembly. As illustrated inFIGS. 5A-5C, the transducer protector 140 is assembled by firstinserting the micro-porous membrane 144 into the second part 152 in aposition in which the micro-porous membrane 144 is disposed within thesecond portion 153 of the vent assembly compartment 142. In thisposition, as shown in FIG. 5A, the micro-porous membrane 144 is seatedagainst a ledge 156 that is defined by the second part 152. Themicro-porous membrane 144 can be dimensioned such that a press-fit isprovided between the micro-porous membrane 144 and the sidewall 155 ofthe second part 152 of the transducer protector 140. Next, asillustrated in FIG. 5B, the self-sealing vent structure 146 ispositioned adjacent the micro-porous membrane 144 in a position in whichthe self-sealing vent structure 146 is partially disposed within thesecond portion 153 of the vent assembly compartment 142. Theself-sealing vent structure 146 can also be dimensioned such that apress-fit is provided between the vent structure 146 and the sidewall155 of the second part 152 of the transducer protector 140. Then, asillustrated in FIG. 5C, the first part 150 can be connected to thesecond part 152 of the transducer protector 140 such that the respectivesidewalls 154, 155 of the first and second parts 150, 152 of thetransducer protector 140 together define the vent assembly compartment142. The first and second parts 150, 152 of the transducer protector 140can be bonded to each other, such as by welding, adhering (e.g., withepoxy), solvent bonding, mating threaded connections or other suitablemethod.

Referring to FIGS. 6A and 6B, pressure can be read out and displayedthrough the electronics of the dialysis machine 50. Dynamic pressurepulse variations may take place, and will be transmitted through tubingsections 110, 140 to the pressure transducer 130, for a continuouspressure measurement. The measured pressure pattern is compared to amachine pressure pattern, which is determined as a function of pumpoperation. If there is a variance between the measured pressure patternand the machine pressure pattern automatic shut-off can occur and/or analarm can be sounded. If, for example, the micro-porous membrane 144ruptures, thereby allowing liquid (e.g., blood) to contact theself-sealing vent structure 146, the vent structure 146 will self sealand inhibit (e.g., prevent) fluid, including gases, from passing. As aresult, as illustrated in FIG. 6B, the pressure transducer 130 willsense a change in the pressure pattern (e.g., a diminished pressurepulse), which the associated dialysis machine electronics will interpretas a possible membrane rupture.

Air Release Chamber

Referring to FIGS. 7, 7A, 7B and 7C, the air release chamber 230 issubstantially hollow for filling with a liquid. The chamber 230 can beused for removing gas (e.g., air bubbles) from blood. The chamber 230has a bottom region 234 and a top region 236, where the bottom and topare relative to the chamber's orientation during use. An entry port 240and an exit port 242 are in the bottom region 234 of the chamber 230. Insome implementations, the ports 240, 242 are located in a bottom surfaceof the chamber 230. In other implementations, as shown in FIG. 7F, atleast one of the ports 240, 242 is located in a side surface of thechamber 230. In some implementations, a dam 248 is between the ports240, 242. The dam 248 extends at least part way from one side wall to anopposite side wall. In some implementations, the dam 268 contacts eachside wall so that all fluid entering entry port 240 flows over the topof the dam 248 before flowing out the exit port 242. In someimplementations, a clot filter 254 is positioned adjacent to the exitport 242. Fluid flows through the clot filter 254 prior to flowing outof the exit port 242. In some implementations, the clot filter 245 has aporosity of about 50 microns to about 500 microns.

The ports 240, 242 are holes in the chamber 230 which can be in fluidcommunication with tubular shaped extensions. The extensions are able tobe connected to tubes, such as by pressure fitting or bonding. Theextensions can be integrally formed with the chamber 230 or subsequentlyattached to the chamber 230, such as by bonding or welding.

At the top region 236 of the chamber 230 is a self-sealing vent assembly270. The self-sealing vent assembly 270 includes a micro-porous membrane260 and a vent structure 264. The assembly with the vent structure 264and micro-porous membrane 260 may provide reduced condensation orminimize condensation on the micro-porous membrane 260. The micro-porousmembrane 260 allows gas (e.g., from air bubbles in the blood) to ventfrom the chamber 230. Pores in the micro-porous membrane 260 are smallenough to keep foreign particles and organisms from entering the chamber230 from the outside air.

In some implementations, the membrane 260 includes a hydrophobicmaterial, such polytetrafluoroethylene (PTFE) (e.g., expandedpolytetrafluoroethylene (ePTFE)) In some embodiments, the membrane 260is a fibrous carrier with a matted and woven layer on top of which ePTFEor other micro-porous material is applied. The hydrophobic micro-porousmembrane 260 keeps liquid from leaking out of the chamber 230 when thechamber 230 is substantially filled with liquid and allow air to passthrough. A suitable membrane has an average pore size of about 0.05microns to about 0.45 microns (e.g., about 0.22 microns, about 0.2microns). Suitable membranes are available from Pall Corporation, EastHills, N.Y., under the Versapor® mark and from W. L. Gore & Associates,Inc., Newark, Del.

The vent structure 264 is a solid porous block, having an average poresize of about 15 micron to about 45 microns, that allows air to passthrough and escape from the chamber. The vent structure 264 is also aself-sealing vent structure. In some implementations, the vent structure264 is formed of a blend of polyethylene (e.g., high densitypolyethylene (HDPE)) and carboxymethylcellulose (CMC), a blend ofpolystyrene and methyl-ethyl-cellulose or of polypropylene- orpolyethylene-based porous material. Such materials are available fromPorex Corporation, Fairburn, Ga., such as EXP-816, which is a productcontaining 90% by weight polyethylene and 10% by weightcarboxymethylcellulose with an average pore size of about 30 microns toabout 40 microns. However, other percentages of the materials can beused, as well as other materials and other pore sizes. For example, thevent structure 264 can include about 80% to about 95% by weight highdensity polyethylene and about 5% to about 20% by weightcarboxymethylcellulose.

When the vent structure 264 comes into contact with liquid, e.g.,humidity or moisture, the swelling agent (e.g., cellulose component,e.g., carboxymethylcellulose) of the vent structure expands, therebyclosing off the pores in the polymer component (e.g., high densitypolyethylene) of the vent structure 264. The vent structure 264 ismounted adjacent to and just above the membrane 260 so that thehydrophobic membrane 260 is located between the vent structure 264 andthe chamber 230. The vent structure 264 inhibits (e.g., prevents)condensation from accumulating on and contacting the membrane 260. Insome embodiments, the vent structure 264 directly contacts the membrane260. The vent structure 264 can be substantially disc shaped or can beanother shape that is compatible with a chamber on which the ventstructure 264 is mounted. In embodiments, the vent structure 264 isabout 0.1 mm to about 10 mm thick.

When the chamber 230 is filled with blood, inhibiting (e.g., preventing)the protein in the blood from accumulating on the membrane 260 canmaintain the hydrophobic characteristic of the membrane 260. Whole bloodcan be kept from the membrane 260 by providing a barrier between theblood and the membrane 260, such as a liquid barrier 268, as describedfurther below. The height of the chamber 230 is sufficient to maintainthis barrier 268 and inhibits (e.g., prevents) the liquid above thebarrier 268 from substantially mixing with liquid below the barrier 268.

The shape of the chamber is approximately elongate. In someimplementations, such as those shown in FIGS. 7 and 7D, the bottomregion 234 of the chamber 230, 230′ is wider than the top region 236,such that the chamber 230, 230′ has a quasi-conical shape or a flare atthe bottom. In some implementations, such as those shown in FIG. 7E, thetop and bottom dimensions of the chamber 230″ are approximately equal sothat the chamber 230″ has a rectangular or cylindrical shape. The bottomregion 234 can also be narrower than the top region 236. If the ports240, 242 are in the bottom surface of the chamber, the bottom surfacehas a sufficiently large dimension to accommodate the ports 240, 242 aswell as any tubes coupled to the ports for directing fluid into and outof the chamber. For example, if the tubing has an outer diameter of 6.25mm, the bottom surface is at least 12.5 mm wide. The chamber 230 issized to maintain the liquid barrier 268. In some implementations, thechamber 230 is at least about two inches in height, (e.g., about threeto about four inches).

The chamber is formed of a material suitable for medical devices, thatis, a medical grade material. Plastics, such as polyvinylchloride,polycarbonate, polyolefins, polypropylene, polyethylene or othersuitable medical grade plastic can be used because of their ease ofmanufacturing, ready availability and disposable nature. The chamber isformed, such as by molding, for example, extruding, blow molding orinjection molding. The chamber can be formed of a transparent or clearmaterial so that the liquid flowing through the chamber can be observed.

The construction of the vent assembly 270 is described with respect tothe following figures. Referring to FIGS. 8 and 8A, a ring 302 holds themicro-porous membrane 260 within its inner diameter. The ring can beformed of plastic, such as one of the plastics described herein. Themicro-porous membrane 260 can be insert-molded into the ring 302. Thatis, the micro-porous membrane 260 can be placed into a mold and held inplace. The plastic for the ring 302, which can be polyethylene,polystyrene or another other suitable material, is then injected into amold to form the ring 302. The ring 302 has an inner diameter z and anouter diameter y. Referring to FIGS. 9 and 9A, the vent structure 264has a diameter of z.

Referring to FIGS. 10 and 10A, an insert 312 is configured to hold thering 302 and the vent structure 264. The insert 312 has a first portion314 and a second portion 316. The first portion 314 has a greater outerdiameter and greater inner diameter than the outer diameter and innerdiameter of the second portion 316. In some embodiments, the innerdiameter of the first portion 314 is y and the outer diameter of thesecond portion 316 is x. The transition between the first portion 314and the second portion 316 forms a ledge. The insert 312 can be formedof the same plastic or a different material from the plastic ring.

Referring to FIGS. 11 and 11A, a retainer 318 is configured to hold thering 302, the vent structure 264 and the insert 312. In someembodiments, the retainer 318 has a constant outer diameter, that is,the outer diameter does not change from one end of the retainer 318 tothe other. In some embodiments, the retainer 318 has three unique innerdiameters. Near the top (as shown in the figure) of the retainer 318,the inner diameter is the greatest and in some embodiments, the innerdiameter is equal to or just slightly greater than the outer diameter ofthe first portion 314 of the insert 312. Near the bottom of the retainer318, the retainer 318 can have an inner diameter that is less than z, orless than the diameter of the vent structure 264. Between the bottom andthe top of the retainer 318, the inner diameter can be about equal to x,that is, about equal to or slightly greater than the outer diameter ofthe second portion 316 of insert 312.

Referring to FIG. 12, an assembly 300 can be formed from the ring 302,vent structure 264, insert 312 and retainer 318. The retainer 318 holdsthe vent structure 264 so that the portion of the retainer with an theinner diameter that is less than the vent structure's diameter inhibits(e.g., prevents) the vent structure 306 from escaping. The ring 302 iswithin the inner diameter of the retainer 318 and adjacent to the ventstructure 264. In some embodiments, the ring 302 has sufficient heightthat the vent structure 264 can be seated within the inner diameter ofthe ring 302. The first portion 314 of the insert 312 fits between theouter diameter of the ring 302 and the inner diameter of the retainer318. The retainer 318 can be bonded to the insert 312, such as bywelding, adhering, solvent-bonding or other suitable method. The secondportion 316 of the insert 312 forms a shank that is sized to fit into achamber, as described further herein.

Referring to FIG. 13, the chamber can be formed from two parts. A twoport cap 322 can form a bottom of the chamber. A gravity chamber 324 canform the top of the chamber. Referring to FIG. 14, when the cap 322 andgravity chamber 324 are brought together, they form a chamber body 326.The top of the chamber body 326 is sized so that the shank of theassembly 300 can be fit into the chamber body 326, as shown in FIGS. 15and 16. The chamber body 326 and the assembly 300 can be sealedtogether, such as by welding, adhering, solvent-bonding or othersuitable method.

In other implementations, a different type of assembly can be formed.Referring to FIGS. 17, 17A and 17B, for example, a support 328 can havean inner diameter in which the micro-porous membrane 260 is held. Theinner diameter of the support 328 can be x. The support 328 can have aflange that extends outwardly from the outer diameter at a top of thesupport 328. As shown in FIG. 18, the vent structure 264 can fit withinthe support 328 and on the micro-porous membrane 260. The micro-porousmembrane 264 can be insert-molded into the support 328. The ventstructure 264 can be press-fit into the support 328. Referring to FIGS.19, 20 and 21, the support 328 is sized so that the support 328 fitsinto a chamber body 326 with the flange extending beyond the innerdiameter of the chamber body 326 to inhibit (e.g., (prevent) the support328 from being pressed in or falling into the chamber body 326.

Although the vent assemblies described herein are shown as cylindrical,the assembly can have other shapes as well, such as rectangular,polygon, triangular or other suitable cross sectional shapes. Also, thevent assembly can have a threaded portion so that the assembly can be,for example, screwed into the air release chamber. Alternatively, thevent assembly can be welded, adhered with epoxy or otherwise fastened tothe top of the chamber.

Methods of Operation

Referring to FIGS. 1 and 22, the air release chamber 230 is in line inthe extracorporeal fluid circuit of a system for fluid filtration andair removal. A first liquid that is compatible with the liquid to befiltered (the second liquid) is introduced into the system to prime thesystem (step 404). In hemodialysis, the first liquid is a bloodcompatible solution, such as saline. The saline flows through thearterial tubing 110 to the arterial pressure sensor assembly120 so thatthe pressure of the liquid flowing through the circuit 100 on thearterial side can be monitored, as described above. The saline thenflows through a portion of the channel that abuts the pump 160. The pump160 forces the saline through the circuit 100. The saline then flows tothe dialyzer 170. Next, the saline, or the first liquid, flows throughthe entry port 242 of the chamber 230 and fills the chamber (step 412).To fill the chamber completely, venous line 190 can be clamped to createa positive pressure once the saline is introduced into the chamber 230.Air is forced out the top of the chamber 230 and through themicro-porous membrane 260 and vent structure 264 as saline fills thechamber 230. The saline contacts the membrane 260 and the chamber 230 issubstantially free of air once the chamber 230 is completely filled.However, the saline does not exit through the membrane 260, because themembrane 260 is hydrophobic. After the venous line 190 is unclamped, thesaline exits through the exit port of the chamber and out the venousline 190.

The second liquid, such as a bodily fluid, for example, blood, is thenintroduced into the system (step 418). The blood follows the same routeas the saline and, for the most part, pushes the saline through thecircuit 100. When the blood enters the chamber 230, the blood forces thesaline at the bottom of the chamber 230 through the exit port (step422). However, the blood does not displace all of the saline within thechamber 230. Because of the height of the chamber 230, the blood entersthe chamber 230 and only traverses part of the height of the chamber 230before flowing back down along flow path 274 to the exit port (as shownin the air release chamber formed of transparent material in FIG. 23).An interface 268 between the saline and the blood delineates thefurthest extent of most of the blood within the chamber 230. Theinterface 268 between the blood and saline can visually be observed andstretches across the entire width of the chamber. Because blood andsaline are not immiscible, there is some amount of mixing between thetwo fluids around the interface 268.

The saline keeps the blood from contacting the filter 260. However, apercentage of blood can be present in the saline without hindering theoperation of the circuit 100. That is, the saline need not be completelyfree from blood for the air release chamber 230 to both allow gas (e.g.,from air bubbles in the blood) to vent from the circuit 100 and retainthe liquid in the circuit 100. The solution that is mostly salinesubstantially protects the membrane 260 from becoming coated withprotein. If the chamber 230 is sufficiently elongated, the blood doesnot mix with the saline at the top portion of the chamber 230 becausethe saline remains relatively stagnant as the blood flows through thechamber 230.

Any unbound gas, or air, that is in the blood, such as air that isintroduced by the dialyzer 170 or air that comes out of solution fromthe blood, rises as tiny air bubbles within the blood and saline untilthe air eventually vents out through the vent assembly 270, includingthe micro-porous filter 260 and the vent structure (step 430). With adam 248 inside of the chamber 230, the blood travels up and over the dam248 rather than straight across the bottom of the chamber 230 out theexit port 242. By directing the flow of blood upwards, the blood withair is not able to flow in and directly back out of the chamber 230without flowing upwards to at least a height greater then the height ofthe dam 248. The surface area of the dam 248 and the inner walls of thechamber 230 enables air, including microbubbles, to separate from theblood and exit the circuit 100 through the micro-porous membrane 260.

Throughout the circuit, the blood flows without there being asubstantial air-blood interface. Although the blood does not come intocontact with air and thus clotting is less likely to occur, the bloodcan pass through an optional filter in the chamber. In someimplementations, after exiting the chamber, the blood passes by orthrough one or more sensors, such as temperature or air detectingsensors.

Other Embodiments

While certain embodiments have been described above, other embodimentsare possible.

As an example, although an embodiment of a extracorporeal circuit hasbeen described in which an arterial pressure sensor assembly is arrangedto measure a pre-pump arterial pressure, in some embodiments, asillustrated in FIG. 24, an arterial pressure assembly 120′ can,alternatively or additionally, be positioned downstream of the pump 160for post pump arterial pressure measurement. In some embodiments, thecircuit 100 can also include a venous pressure sensor assembly 182 incommunication with the venous tubing 180, for monitoring the pressure ofliquid (e.g., blood) flowing through the circuit 100 on the venous side.The venous pressure sensor assembly 182 can have the same constructionas the arterial pressure sensor assembly 120 described above with regardto FIGS. 3A-5C.

In some implementations, the vent assembly can include a multilayerself-sealing vent structure, where different layers of the ventstructure have differing self-sealing (e.g., swelling) characteristics.For example, FIG. 25 shows (in cross-section) a vent assembly 270′including a multilayer self-sealing vent structure 264′. The multilayerself-sealing vent structure 264′ includes a first porous layer 265disposed adjacent the micro-porous membrane 260, and a second porouslayer 266 disposed adjacent to the first porous layer 265. The firstporous layer 265 is a solid porous block, having an average pore size ofabout 5 microns to about 45 microns, e.g., about 10 microns. In someembodiments, the first porous layer 265 can be formed of polyethylene(e.g., high density polyethylene (HDPE)), polystyrene, or ofpolypropylene- or polyethylene-based porous material. Such materials areavailable from Porex Corporation, Fairburn, Ga. The first porous layer265 is about 3 mm to about 5 mm thick, e.g., about 4 mm thick. In someembodiments, the first porous layer 265 can be self-sealing. In someembodiments, for example, the first porous layer 265 may include arelatively small amount of carboxymethylcellulose, e.g., about 0% toabout 10% by weight carboxymethylcellulose.

The second porous layer 266 is a solid porous block, having an averagepore size of about 15 to about 45 microns, e.g., about 30 microns. Thesecond porous layer 266 is about 3 mm to about 5 mm thick, e.g., about0.4 mm thick. The second porous layer 266 is self-sealing, and isrelatively more responsive to the presence of moisture that the firstporous layer 265; i.e., the second porous layer 266 has a greaterpropensity to self-seal (e.g., swell) in the presence of moisture thanthe first porous layer 265. In some embodiments, the second porous layer266 is formed of a blend of polyethylene (e.g., high densitypolyethylene (HDPE)) and carboxymethylcellulose (CMC), a blend ofpolystyrene and methyl-ethyl-cellulose or of polypropylene- orpolyethylene-based porous material. Such materials are available fromPorex Corporation, Fairburn, Ga., such as EXP-816, which is a productcontaining 90% by weight polyethylene and 10% by weightcarboxymethylcellulose with an average pore size of about 30 microns toabout 40 microns. However, other percentages of the materials can beused, as well as other materials and other pore sizes.

During use, condensation can, for example, form within the ventassembly. The first porous layer 265 allows for a small amount ofcondensation to be compensated for without activation of theself-sealing property of the second porous layer 266. The first porouslayer 265, being relatively less responsive to the presence of moisture(i.e., as compared to the second porous layer 266) slows the progressionof moisture from within the chamber 230 toward the second porous layer266. The first porous layer 265 provides additional surface area (e.g.,within pores) where condensation can be pulled out of the air exitingthe vent assembly 270′ before it reaches self-sealing, second porouslayer 266. Thus, small amounts of humidity and moisture (e.g.,condensation) from within the air release chamber 230 can be compensatedfor without triggering closure of the self-sealing vent.

In some embodiments, the air release chamber and one or more othercomponents can be incorporated into an integrated fluid circuit. Theintegrated fluid circuit has the components described above, such as theair release chamber, formed together in one assembly or integratedmolding rather than discrete separate or modular devices. The integratedfluid circuit is adapted to removably seat into a machine, such as ablood purification machine, like a hemodialysis machine The integratedfluid circuit is similar to a cassette or cartridge, where an operatormerely snaps the integrated fluid circuit into the machine and afterjust a few additional connections, begins operation.

Referring to FIG. 26, the integrated fluid circuit 512 has a rigid body518 and a flexible backing (not shown). The rigid body has asubstantially flat surface 520 with one or more concave (when viewedfrom the backside) portions or recessed portions protruding from a frontsurface of the body 518. The flexible backing can be applied so that thebacking covers only the recessed portions or so that the backing coversmore than just the recessed portions, up to all of the back surface ofthe rigid body.

The integrated fluid circuit has a recessed portion that serves as theair release chamber 526. As with the chamber described above, the airrelease chamber 526 includes a self-sealing vent assembly 570 at a topregion and optionally includes a dam 560 and a clot filter 568. The ventassembly 570 can be formed separately from the body 518 and fit into thetop of the air release chamber 526, similar to the method described withrespect to forming the devices shown in FIGS. 16 and 21. Alternatively,a micro-porous membrane and vent structure can be fit into theintegrated fluid circuit after the body 518 has been formed, without asupport or retainer.

A first channel 534 in rigid body 518 leads from an edge of the rigidbody 518 to a bottom region of the air release chamber 526. Over oneportion of the channel 534, a venous recess or pocket 548 is formed. Theflexible backing backs the venous pocket 548. The venous pocket 548 issized so that a transducer in the machine can measure the venous fluidpressure through the flexible backing. A second channel 578 extends fromthe outlet of the air release chamber 526 to an edge of the rigid body518. The first and second channels extend to the same or different edgesof the rigid body 518. The first channel 534 and second channel 578 arein fluid communication with the air release chamber 526.

In some implementations, a third channel 584 is formed in the rigid body518. The third channel 584 is not in fluid communication with the firstor second channels when the integrated fluid circuit is not in themachine or connected to a dialyzer. In some implementations, an arterialpocket 588 is formed along the third channel 584. The arterial fluidpressure can be measured through the flexible backing of the arterialpocket 588. One end of the third channel 584 extends to one edge of therigid body 518 and the other end extends to the same or a differentedge, as shown in FIG. 26.

Optionally, a fourth channel 592 extends across the rigid body 518. Apost-pump arterial pocket 562 overlaps the fourth channel 592. In someimplementations, additional recesses and channels are formed in therigid body.

In some implementations, tubes 594 a, 594 b, 594 c, 594 d and 594 e areconnected to the rigid body 518, such as at the locations where thefirst, second, third and fourth channels extend to the edges. The tubesare connected to the rigid body using techniques known in the art. Insome embodiments, the tubes fit into a pre-formed grooves in the rigidbody 518. The tubes can be pressure fitted into the grooves. In otherimplementations, the tubes are clipped onto the rigid body 518.Optionally, at the end of the tubes 594 a, 594 b, 594 c and 594 e arefasteners for connecting the tubes to components of the machine, such asthe dialyzer or to a patient. Tube 594 d wraps around a peristaltic pumpin the machine Tubes 594 a and 594 e connect to a dialyzer. Tubes 594 band 594 c connect to a patient.

Each of the recesses can protrude from the flat surface 520 toapproximately the same distance. Alternatively, some of the recesses,such as the channels, may be shallower than other recesses, such as theair release chamber 526. Referring to FIG. 26A, a cross section of theintegrated circuit 512 shows an outline of the part of chamber 526, theclot filter 568, the side of second channel 578, the membrane 564 and across section of the vent assembly 570. The rigid body 520 can have anoverall thickness of less than about 2 mm, such as less than about 1 mm.Flexible membrane 564 covers the back of the rigid body 520.

In some implementations, instead of one or more of the channels beingformed in the rigid body 518, a tube is connected directly to a featurein the rigid body. For example, instead of forming second channel 578,tube 594 b can be connected directly to the air release chamber 526.

In some implementations, the integrated circuit 512 has two rigid sides.The first rigid side is as described above. The second rigid side issubstantially flat with openings located adjacent to the pockets formedin the first side. The openings are covered with a flexible membrane.

In some implementations, the integrated circuit 512 has posts thatextend from one or more sides of the circuit. The posts can mate withrecesses in the machine, ensuring correct registration of the integratedcircuit 512 with components, such as sensors, in the machine. In someimplementations, the integrated circuit 512 has latches, clips or othersuch device for registering the integrated circuit 512 with the machineand locking the integrated circuit 512 in place.

The machine can have a mechanism that holds the integrated circuit inplace. The mechanism can include a door, a locking device or a suctiondevice for holding the integrated circuit in tight contact with themachine. When the integrated circuit is seated in the machine, pressuretransducers interface with the flexible backing to directly measure thefluid pressure at each of the corresponding locations. Holding theintegrated circuit in contact with the machine allows the pressuretransducers to sense flow through the circuit. Once the integrated fluidcircuit is plugged into the machine and connected with the machine'scomponents, an operator uses the integrated fluid circuit in a mannersimilar to the method of using the circuit chamber 230 described above.

As with the air release chamber 230, the rigid body 518 is constructedof a medical grade material. The flexible backing is constructed from apolymer that is flexible and suitable for medical use, such as anelastomer, including silicon elastomers. Other suitable materialsinclude, high and low density poly ethylene, high and low density polypropylene, separately co-extruded mono layers or multiple layers ofpolyamides, nylons, silicones or other materials commonly known in theart for flexible applications. The backing is attached to the back ofthe rigid body 518, such as by laser, ultrasonic or RF welding or withan adhesive. In some implementations, the backing is attached so thatthe edge of each recess is sealed to the backing. Alternatively, thebacking is attached only at the edge of the rigid body. If the backingdoes not seal the recesses from the flat portions, the machine intowhich the integrated fluid circuit seats is constructed to applysufficient pressure to keep the fluid flowing through the circuit fromleaking out of the recesses and between the backing and the flat surface520. In the back of the rigid portion 518, ridges can be formed whichsurround the recesses. The ridges can aid in sealing the flexiblemembrane to the flat portion 518 when pressure is applied to thecircuit.

In some implementations, injection sites 598 are formed at one or moreof the recesses. The injection sites 598 can be used to inject drugs orsolutions into the fluid. Suitable injection sites 598 are formed ofneoprene gaskets into which a needle can be introduced and removed sothat the gaskets do not leak or weep after the needle is removed.

FIG. 27 shows a perspective view of the integrated fluid circuit 512. Asin FIG. 20, the flexible membrane has been removed from the integratedfluid circuit 512 to show the recesses.

Using the air release chambers described herein in an extracorporealblood circuit inhibits (e.g., prevents) air from contacting bloodflowing through the circuit Inhibiting air in the chamber can reduce thelikelihood of forming clots in the blood. In the event that there is airin the blood before the blood exits the chamber, a hydrophobicmicro-porous membrane and a self-sealing vent structure at the top ofthe chamber allows air that enters the chamber to escape. The membraneand vent structure are part of or connected directly to the air releasechamber. This allows the air to easily escape from the liquid filledchamber. Thus, lines need not be connected to the top of the chamber forwithdrawing air from the circuit.

The self-sealing vent structure of the vent assembly inhibits (e.g.,prevents) moisture or condensation from accumulating on the micro-porousmembrane. The micro-porous membrane can lose its ability to ventefficiently if it gets wet. On occasion, the micro-porous membrane canleak due to becoming wet, which may allow blood to escape the chamber.The vent structure of the vent assembly can inhibit (e.g., prevent) themicro-porous membrane from getting wet and leaking blood to the outsideof the chamber. In the even that the membrane fails, such as due to apuncture, and fluid passes through to the vent structure, the ventstructure swells when it becomes wet. The swollen vent structureinhibits (e.g., prevents) blood from leaking outside of the circuit andinto the atmosphere.

The chamber is first filled with saline before being filled with blood.The chamber has a sufficient height so that after the saline and bloodare introduced into the chamber, the saline is located near the top ofthe chamber and the blood is located near the bottom, and little mixingof the two liquids occurs. The saline inhibits (e.g., prevents) most ofthe proteins in the blood from contacting the micro-porous membrane ofthe vent assembly at the top of the chamber. If protein accumulates onthe micro-porous membrane, the membrane's hydrophobic properties can beinhibited, that is, the membrane can wet, allowing liquid to leak frominside the chamber to outside the chamber. Also, if protein collects onthe membrane, the membrane may become inefficient at allowing air topass through. Thus, a sufficiently long chamber allows the saline tostagnate at the top, inhibiting (e.g., preventing) protein fromcontacting the membrane.

A dam in the chamber between the entry and exit ports may provide asurface for microbubbles to accumulate. The microbubbles in the bloodmay then escape through the chamber rather than passing through the exitport. Reducing clot formation and reducing gas in the blood is safer forthe patient undergoing hemodialysis. The dam also forces the liquids upinto the chamber so that the liquids, and any gases traveling with theliquids, are not immediately pushed out of the chamber before the gascan escape out to the top of the chamber.

Placing components, such as a pocket for taking pressure measurements,channels for fluid flow and the air release chamber, into a singleintegrated fluid circuit eliminates multiples separate components. Fewercomponents are easier for an operator to work with and reduce the riskof operator error. The integrated fluid circuit has a rigid side thatmaintains the integrity of the components, and flexible portions thatallow for taking measurements, such as pressure or temperaturemeasurements. Further, the pockets in the integrated circuit eliminatethe need for pressure sensing lines in fluid communication with the topof the chamber.

The components described herein can be used with other liquids, such asplasma, water, saline, and other medical fluids. Additionally, liquidsother than saline can be used to prime the system. Accordingly, otherembodiments are within the scope of the following claims.

1. An air-release device for allowing air to be released from a liquidin extracorporeal circuitry, the air-release device comprising: anelongate chamber having a bottom region and a top region and a fluidentry port and fluid exit port at or near the bottom region; and a ventstructure at or near the top region of the elongate chamber, the ventstructure comprising a porous material capable of swelling whenmoistened such that the vent structure can inhibit liquid from escapingthe air-release device during use.
 2. The air-release device of claim 1,wherein the vent structure has an average pore size of about 15 micronsto about 45 microns.
 3. The air-release device of claim 1, wherein thevent structure includes polyethylene, polypropylene or polystyrene. 4.The air-release device of claim 1, wherein the vent structure includescarboxymethylcellulose.
 5. The air-release device of claim 1, whereinthe vent structure includes a blend of polyethelene andcarboxymethylcellulose.
 6. The air-release device of claim 1, furthercomprising a microporous membrane adjacent the vent structure at or nearthe top region of the elongate chamber such that liquid can be passedthrough the elongate chamber from the entry port to the exit port so asto at least partially fill the elongate chamber with the liquid whileair exits the chamber via the microporous membrane and the ventstructure.
 7. The air-release device of claim 6, wherein the ventstructure has a thickness greater than a thickness of the micro-porousmembrane.
 8. The air-release device of claim 6, wherein the micro-porousmembrane has an average pore size of about 0.05 microns to about 0.45microns.
 9. The air-release device of claim 6, further comprising a ringinto which the micro-porous membrane is press-fit, wherein the ringsurrounds the vent structure and retains the vent structure adjacent tothe micro-porous membrane.
 10. The air-release device of claim 6,wherein the microporous membrane includes a hydrophobic material. 11.The air-release device of claim 6, wherein the vent structure comprises:a first porous layer; and a second porous layer comprising a porousmaterial capable of swelling when moistened, wherein the first porouslayer is disposed between the micro-porous membrane and the secondporous layer.
 12. The air-release device of claim 11, wherein the firstporous layer comprises a porous material capable of swelling whenmoistened, and the second porous layer is less responsive to moisturethan the first porous layer.
 13. The air-release device of claim 11,wherein the first porous layer has an average pore size of about 5microns to about 45 microns.
 14. The air-release device of claim 11,wherein the second porous layer has an average pore size of about 15 toabout 45 microns.
 15. The air-release device of claim 11, wherein thesecond porous layer has an average pore size that is greater than anaverage pore size of the first porous layer.
 16. The air-release deviceof claim 11, wherein the second porous layer comprises about 5% to about50% by weight carboxymethylcellulose.
 17. The air-release device ofclaim 11, wherein the first porous layer comprises about 0% to about 10%carboxymethylcellulose.
 18. The air-release device of claim 11, whereinthe first porous layer comprises less than 5% carboxymethylcellulose.19. The air-release device of claim 11, wherein the microporous membraneforms at least a portion of a top surface of the elongate chamber. 20.The air-release device of claim 1, wherein the fluid entry and exitports are in a bottom surface of the elongate chamber.
 21. Theair-release device of claim 1, wherein the bottom region of the chamberis flared such that the bottom region is wider than the top region. 22.The air-release device of claim 1, wherein the exit port issubstantially vertically aligned with the vent structure during use, andthe entry port is horizontally offset from the vent structure duringuse.
 23. The air-release device of claim 1, wherein the chamber has aheight of about three inches to about four inches.
 24. The air-releasedevice of claim 1, wherein the extracorporeal circuitry is hemodialysisextracorporeal circuitry.
 25. A dialysis system, comprising: a dialysismachine body; a pump on the machine body; fluid circuitry in fluidcommunication with the pump, wherein the pump is configured to pushfluid through the circuitry; an air release device in fluidcommunication with the fluid circuitry, the air release device beingpositioned adjacent to the machine body, the air release devicecomprising an elongate chamber having a bottom region and a top regionand a fluid entry port and fluid exit port at or near the bottom region;and a vent structure at or near the top region of the elongate chamber,the vent structure comprising a porous material capable of swelling whenmoistened such that the vent structure can inhibit liquid from escapingthe air-release device during use.